Segmental retaining walls commonly comprise courses of modular units (blocks). The blocks are typically made of concrete. The blocks are typically dry-stacked (no mortar or grout is used), and often include one or more features adapted to properly locate adjacent blocks and/or courses with respect to one another, and to provide resistance to shear forces from course to course. The weight of the blocks is typically in the range of ten to one hundred fifty pounds per unit.
Segmental retaining walls commonly are used for architectural and site development applications. Such walls are subjected to high loads exerted by the soil behind the walls. These loads are affected by, among other things, the character of the soil, the presence of water, surcharge, and seismic loads. To handle the loads, segmental retaining wall systems often comprise one or more layers of soil reinforcement material extending from between the courses of blocks back into the soil behind the blocks. The reinforcement material is typically in the form of geosynthetic reinforcement material such as geogrid or geotextile fabric. Geogrids often are configured in a lattice arrangement and are constructed of polymer fibers or processed plastic sheet material (punched and stretched, such as described, for example, in U.S. Pat. No. 4,374,798), while geotextile fabrics are constructed of woven or knitted polymer fibers. These reinforcement members typically extend rearwardly from the wall and into the soil to stabilize the soil against movement and thereby create a more stable soil mass, which results in a more structurally secure retaining wall. In other instances, the reinforcement members comprise tie-back rods that are secured to the wall and which extend back into the soil or into rock.
Although several different forms of reinforcement members have been developed, opportunities for improvement remain with respect to attachment of the reinforcement members to the facing blocks in the retaining wall systems. As a general proposition, the more efficient the block/reinforcement connection, the fewer the layers of reinforcement material that should be required in the wall system. The cost of reinforcing material can be a significant portion of the cost of the wall system, so highly efficient block/reinforcement material connections are desirable.
Many segmental retaining wall system rely primarily upon frictional forces to hold the reinforcement material between adjacent courses of block. The systems may also include locating pins or integral locator/shear resistance features that enhance the block/reinforcement material connection to varying degrees. Examples of such systems include those described in U.S. Pat. Nos. 4,914,876, 5,709,062, and 5,827,015. These systems cannot take advantage of the full tensile strength of the common reinforcement materials, however, because the block/reinforcement material holding forces that can be generated in these systems is typically less than the tensile forces that the reinforcing materials themselves can withstand.
One of the many advantages of segmental retaining wall systems over other types of retaining walls is their flexibility. They do not generally require elaborate foundations, and they can perform well in situations where there is differential settling of the earth, or where frost heaving, for example, occurs. Even so, these types of conditions might result in differentials in the block/reinforcement material connections across the wall in systems that rely primarily on frictional connection of blocks to the reinforcement material.
In an effort to improve the block/reinforcement material connection efficiency, several current retaining wall systems have been developed that mechanically connect the reinforcement members to the blocks. In several such systems, rake shaped connector bars are positioned transversely in the center of the contact area between adjacent stacked blocks with the prongs of the connector bars extending through elongated apertures provided in the reinforcement member to retain it in place. Examples of this type of system are shown in U.S. Pat. Nos. 5,607,262 (FIGS. 1-7), 5,417,523, and 5,540,525.
These systems are only effective if the reinforcement member used is of a construction such that the cross-members that engage the prongs of the connector will resist the tensile forces exerted on the reinforcement member by the soil. There are only a few such reinforcement members currently available and, thus, the wall builder or contractor has to select reinforcement members from a limited number of manufacturers when such an attachment system is used. These systems also rely upon the prongs of the rake connectors being in register with the apertures in the reinforcement member and in contact with cross members of the reinforcement member. If the connector prongs do not line up with the apertures, installation becomes a problem. Variability in the manufacturing process of reinforcement members means that the apertures in this type of reinforcement member frequently are not perfectly regular. A solution to this problem has been to use short connector rakes that only engage several apertures, rather than long connectors that engage all of the apertures in a row across the reinforcement member. This solution eases problems, but would appear to make the connection mechanism less efficient. These devices are subject to the same criticisms as the pure friction connectors.
A third type of connector system uses a channel that, in cross-section, has a relatively large inner portion and a very narrow opening out of that portion. The reinforcement member is provided with a bead or equivalent along its leading edge. The reinforcement member is then threaded into the channel from the side, so that the reinforcement member extends out through the narrow channel opening, but the bead is captured in the larger inner portion. An example of this type of connection is shown in FIGS. 9 and 10 of U.S. Pat. No. 5,607,262. While this system overcomes differential settling concerns, it is very difficult to use in the field, and relies upon special reinforcement member configurations.
A modification of the third type of connector system described above is one in which the channel into which the bead fits is formed by a combination of the lower and adjacent upper block, so that the enlarged/beaded end of the reinforcement member can simply be laid in the partial channel of the lower blocks, and will be captured when the upper blocks are laid. This system simplifies installation, but does not resolve the aforementioned performance concerns. In a variation of this system, the end of a panel of reinforcement material is wrapped around a bar, which is then placed in a hollowed-out portion of the facing unit which is provided with an integral stop to resist pullout of the bar. Rather than being held in place by the next above facing unit, the wrapped bar is then weighted down with earth or gravel fill dumped on top of it in the hollowed out portion of the facing unit. This system is shown in U.S. Pat. No. 5,066,169. Not only is the facing unit of this system extremely complex and difficult to make, but the installation process is difficult and requires the use of very narrow panels of reinforcement material.
A solution to the problems discussed above is disclosed in patent application Ser. Nos. 09/049,627 (filed on May 27, 1998) and 09/487,820 (filed on Jan. 18, 2000), each of which is assigned to Anchor Wall Systems, Inc. The applications disclose retaining wall blocks provided with lock channels and lock flanges that provide a locking mechanism for resisting leaning or toppling of the blocks. A retaining mechanism in the form of a retaining bar interacts with a lock channel formed in the block to retain a geosynthetic reinforcement material within the channel.
A retaining wall constructed with an exterior corner presents unique challenges with respect to the use of geosynthetic reinforcement material. In a generally linear modular retaining wall structure, the forces acting on the wall tend to act in a single direction, i.e. in a direction tending to topple the wall forward. Therefore, geosynthetic reinforcement material connected to the blocks forming the linear wall and extending rearwardly from the wall and into the soil provides acceptable stability. However, with an exterior corner, the pressures resulting from the soil, surcharge, and seismic loads, are exerted on both walls of an exterior corner. Therefore, to achieve the maximum benefits from the geosynthetic reinforcement material and provide adequate stability adjacent an exterior corner, the geosynthetic reinforcement material should be connected to the blocks that form the right and left sides of an exterior corner.
An additional factor to be considered when constructing a segmental retaining wall structure is the need to offset the vertical joints in each course from the vertical joints in the courses located above and below each course. Alignment of the vertical joints in a wall is generally thought to detract from the appearance of the resulting wall structure, and it is typically common in the art to avoid vertical joint alignment.
The need to avoid vertical joint alignment in the courses of the wall structure presents difficulties at an exterior corner. First, uniform-sized corner blocks often cannot be used, due to setback of the blocks in the remaining wall structure. In addition, the blocks that form the exterior corner must also be constructed and positioned to prevent vertical joint alignment.
It can therefore be appreciated that there exists a need for a corner block, for use in a retaining wall having an exterior corner, that is constructed to permit interaction with geosynthetic reinforcement material so as to stabilize both the right and left sides of the corner, and which does not have vertical alignment of joints.